1. Field
The present disclosure relates to a fuel cell stack.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell includes a unit cell including a membrane electrode assembly (MEA) and separators sandwiching the MEA therebetween. The MEA includes an electrolyte membrane made from a polymer ion-exchange membrane, an anode electrode disposed on one side of the electrolyte membrane, and a cathode electrode disposed on the other side of the electrolyte membrane. Typically, a predetermined number of unit cells of this type are stacked and used as a vehicle fuel cell stack.
In the fuel cell, a fuel gas channel is formed in a surface of one of the separators so as to supply a fuel gas toward the anode electrode and an oxidant gas channel is formed in a surface of the other separator so as to supply an oxidant gas toward the cathode electrode. Moreover, a coolant channel is formed between adjacent separators of adjacent fuel cells so that a coolant can flow along surfaces of the separators to a region in which the electrodes are disposed.
A fuel cell of this type is usually structured as a so-called internal-manifold-type fuel cell. The internal-manifold-type fuel cell has a fuel gas inlet manifold and a fuel gas outlet manifold, through which a fuel gas flows; an oxidant gas inlet manifold and an oxidant gas outlet manifold, through which an oxidant gas flows; and a coolant inlet manifold and a coolant outlet manifold, through which a coolant flows. All of these manifolds extend in the stacking direction of the unit cells.
However, internal-manifold-type fuel cells have a problem in that a reactant gas is nonuniformly supplied to the entire surface of the reactant gas channel from the reactant gas inlet manifold. Japanese Unexamined Patent Application Publication No. 2008-293743, for example, discloses a fuel cell to address this problem.
The fuel cell includes a membrane electrode assembly and a separator that are stacked, the membrane electrode assembly including an electrolyte membrane and a pair of electrodes sandwiching the electrolyte membrane therebetween; a reactant gas channel through which a reactant gas is supplied along a surface of each of the electrodes, and a reactant gas manifold through which the reactant gas flows in the stacking direction.
The separator includes an inlet buffer portion and a supply-side of the reactant gas manifold. The inlet buffer portion is located at an inlet side of the reactant gas channel, has a substantially triangular shape, and has a width substantially the same as the width of the reactant gas channel field. The supply-side of the reactant gas manifold is located near one of ridge lines of the inlet buffer portion. The inlet buffer portion has protrusions. The disposition density of the protrusions in a middle portion of the inlet buffer portion is lower than the disposition density of the protrusions in end portions of the inlet buffer portion.
The reactant gas easily passes through a middle portion of the inlet buffer portion in the width direction, and the disposition density of the protrusions is low in the middle portion of the inlet buffer portion. Therefore, the flow speed of the reactant gas decreases in the middle portion and the reactant gas can be guided to channel grooves in a middle portion of the reactant gas channel in the width direction.